CNBC's Brian Sullivan reports Senate GOP leaders say they don't have enough votes to stop witnesses from appearing at the impeachment trial of Pres. Donald Trump.

President Donald Trump’s impeachment trial in the Senate is set to resume Wednesday afternoon, with the upper chamber poised to question his legal team and the House managers.

The new phase comes after the early completion of oral arguments from Trump’s defense team on Tuesday. The team, led by White House counsel Pat Cipollone and Trump’s personal lawyer Jay Sekulow, used approximately half of its allotted 24 hours to lay out the case for acquittal and urge senators not to call additional witnesses. Here’s what to expect:

The Senate reconvenes at 1 p.m. ET Wednesday. Senators will have 16 hours over two days to ask questions of the House managers and the defense team.
Questions will be submitted in writing on small cards, and Chief Justice John Roberts, who is presiding over the trial, will read each question out loud, along with the name of the senator who asked it.
Republicans and Democrats will have an equal opportunity to ask questions, and Roberts is expected to alternate between the two when posing the questions.
In arguments Tuesday, Sekulow addressed for the first time a bombshell report revolving around former national security advisor John Bolton, whom House Democrats are pushing to have subpoenaed as a witness.

According to Bolton’s upcoming memoir, “The Room Where It Happened,” Trump told him in person last summer that he planned to withhold nearly $400 million in U.S. foreign aid to Ukraine until the country agreed to launch investigations into Trump’s political rivals, most notably, former Vice President Joe Biden and his son Hunter.

The relationship between the abruptly halted aid and the investigations Trump wanted is at the heart of the impeachment case.

Trump’s lawyers have insisted the two issues were entirely separate, and the aid was not being withheld to exercise leverage over the Ukrainian president. On Tuesday, they also argued that Bolton’s book amounted to an “inadmissible” allegation.

“You cannot impeach a president on an unsourced allegation,” Sekulow said Tuesday, although, notably, he did not deny the facts contained in Bolton’s account.

Read more: Trump impeachment trial: Defense wraps up oral arguments, urges Senate to acquit the president

Trump has denied that he ever told Bolton the release of aid was dependent upon the launch of investigations. On Wednesday morning, the president went a step further, attacking Bolton in a series of tweets, calling his former advisor’s memoir “nasty & untrue” and claiming without evidence that it contains “All Classified National Security” material.

Following this past weekend’s revelations about the Bolton book, moderate Republicans like Sens. Mitt Romney of Utah and Susan Collins of Maine signaled an increased interest in voting to allow witness testimony at Trump’s Senate trial.

The GOP holds a 53-47 majority in the Senate, so Democrats would need four Republicans to join with them and vote to call new witnesses. Two additional potential GOP defectors are Alaska Sen. Lisa Murkowski and retiring Tennessee Sen Lamar Alexander. Neither has signaled how they plan to vote on witnesses.

Following Tuesday’s trial proceedings, Senate Majority Leader Mitch McConnell, R-Ky., said a preliminary vote count among senators indicated that the GOP does not have enough votes to block witnesses or additional documents.

Moderate Democratic Sen. Joe Manchin of West Virginia said in an interview Wednesday morning that he would consider Hunter Biden to be a relevant witness, effectively floating the idea of a swap — Bolton’s testimony, which would ostensibly harm the president’s case, for Biden’s, which some senators think could help it.

Even if witnesses are called, it remains unlikely that the Senate will vote to convict Trump and remove him from office.

The Senate is expected to vote Friday on whether to call witnesses or subpoena additional documents.

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